The unique characteristics of lenses of dielectric materials with variable refractive indices (Luneberg, Maxwell, Eaton and others ) particularly their practically unlimited wide-angle, multi-channel and wide-band characteristics, predetermines the possibility of their effective adoption in multi-channel communications systems, television and radar.
However, wide adoption of the lenses is inhibited by their high cost, since the construction of existing lenses with variable refractive index, which ensure changes in dielectric permittivity with a high degree of accuracy in corresponding to the desired principle, are extremely labor-intensive and demand a large amount of manual labor in production.
Spherical lenses with variable refractive index containing an assembly of covers of a single dielectric are well-known. The dielectric permittivity .di-elect cons. and thickness of each cover is selected to approximate with maximal precision the necessary continuous changes of .di-elect cons. along the lens radius ( Antenna Engineering Handbook, McGraw-Hill Book Co., New York, 1984; Skolnik M. J. Introduction to Radar Systems , McGraw-Hill Book Co., New York, 1980.)
However, for the spherical lenses described above, with an increase in operating frequency, together with the necessary decrease in the absolute layer thickness, there is an increased requirement for precision in construction of the spherical surface and the tolerance for deviations in the value of .di-elect cons. becomes more rigid, which significantly complicates the manufacturing process and increases its, particularly for short wave band and short-wave portion of microwave band.
In addition, a design for spherical dielectric lenses with variable refractive index is known. These lenses contain cubic modules identical in size, with the exclusion of the exterior modules, made from homogeneous dielectric with various values of dielectric permittivity, arranged in horizontal layers parallel to one another in accordance with the principle of change of dielectric permittivity. In these lenses, the cubic modules are connected with one another with an adhesive paste material (Shrank H. E.- In Proc. 7th Electrical Insulation Conf., New York, 1967, 15-19/x).
The properties of the lenses described are significantly better in comparison with analogous lenses, since it is possible to finish modules which are unsatisfactory due to their refractive characteristics, homogeneity or isotropic characteristics.
Furthermore, to ensure the required illumination properties, in lenses of the same diameter a much lower gradation in size of the cubic modules is required, in comparison with the number of covers of spherical form. Thus, for example, the nine-layers lens is equivalent in its properties to the lens created from cubic modules, which has all of four gradations in value .di-elect cons. (Proc. Int. Conf. on Radar, China, 1986 4-7/XI, Suppl., pp. 1-53).
However, in the body of such a lens there are a large quantity of extended discontinuities, formed by the gradations between the modules and the gradations between the module layers, and also discontinuities formed by the adhesive interlayers, which produce additional losses in the lens gain to energy dispersion of up to 2 dB or more, while the regular character of the fraction of discontinuities leads to a frequency dependence of the gain oriented within these same limits. In addition, assembly of the spherical lens is complex and labor-intensive with the adoption of the adhesive composite.